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SubjectRE: [PATCH v5 1/2] clk: Add of_clk_get_by_name_optional() function
Date
Hi Stephen,

On 03 September 2018 10:33 Phil Edworthy wrote:
> On 01 September 2018 03:46, Stephen Boyd wrote:
> > Quoting Phil Edworthy (2018-08-31 07:07:22)
> > > diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c index
> > > 9ab3db8..4adb99e 100644
> > > --- a/drivers/clk/clkdev.c
> > > +++ b/drivers/clk/clkdev.c
> > > @@ -54,30 +54,29 @@ EXPORT_SYMBOL(of_clk_get);
> > >
> > > static struct clk *__of_clk_get_by_name(struct device_node *np,
> > > const char *dev_id,
> > > - const char *name)
> > > + const char *name,
> > > + bool optional)
> > > {
> > > struct clk *clk = ERR_PTR(-ENOENT);
> > > + struct device_node *child = np;
> > > + int index = 0;
> > >
> > > /* Walk up the tree of devices looking for a clock that matches */
> > > while (np) {
> > > - int index = 0;
> > >
> > > /*
> > > * For named clocks, first look up the name in the
> > > * "clock-names" property. If it cannot be found, then
> > > - * index will be an error code, and of_clk_get() will fail.
> > > + * index will be an error code.
> > > */
> > > if (name)
> > > index = of_property_match_string(np, "clock-names",
> name);
> > > - clk = __of_clk_get(np, index, dev_id, name);
> > > - if (!IS_ERR(clk)) {
> > > - break;
> > > - } else if (name && index >= 0) {
> > > - if (PTR_ERR(clk) != -EPROBE_DEFER)
> > > - pr_err("ERROR: could not get clock %pOF:%s(%i)\n",
> > > - np, name ? name : "", index);
> > > + if (index >= 0)
> > > + clk = __of_clk_get(np, index, dev_id, name);
> > > + if (!IS_ERR(clk))
> >
> > Was this change necessary? It looks like we can leave it all alone and keep
> > passing a negative number to __of_clk_get() and have that return an error
> > pointer which we then return immediately as an error. But, if the clock is
> > optional and we've passed a name here, shouldn't we treat an error from
> > of_property_match_string() as success too? This is all looking pretty fragile
> so
> > maybe it can be better commented and also more explicit instead of relying
> > on the reader to jump through all the function calls to figure out what the
> > return value is in some cases.
> If we call __of_clk_get, with index < 0, we will not be able to differentiate
> between clock provider not present and other errors with the passed data,
> as it will just return -EINVAL.
>
> of_property_match_string() will return -EINVAL if the "clock-names"
> property
> is missing, or -ENODATA if the specified clock name in the "clock-names"
> property is missing. That is why I have changed the code to conditionally
> call __of_clk_get, so the code will correctly treat optional clocks that are not
> present.
When getting named optional clocks, if the node has a "clock-names" property,
but no clock matching the name we want, I think the function should stop there
and *not* walk up the tree of devices looking for a matching clock. In this case,
the code determines that the optional clock is not present.

If there isn’t a "clock-names" property in the current node, the function should
walk up the tree of devices looking for a matching optional clock. If there are no
parent nodes left and we haven't found a matching optional clock, we determine
that the clock isn’t there.

Is that how this should work?

Thanks
Phil


> > > return clk;
> > > - }
> > > + if (name && index >= 0)
> > > + break;
> >
> > And this causes us to duplicate logic down below because we have to check
> it
> > again if it's not optional or some other error condition?
> Yes, the error handling is messy, though I have tried to make this simple.
> I'll have a think about some other way to make this cleaner.
>
>
> > >
> > > /*
> > > * No matching clock found on this node. If the
> > > parent node @@ -89,6 +88,16 @@ static struct clk
> > *__of_clk_get_by_name(struct device_node *np,
> > > break;
> > > }
> > >
> > > + /* The clock is not valid, but it could be optional or deferred */
> > > + if (optional && PTR_ERR(clk) == -ENOENT) {
> > > + clk = NULL;
> > > + pr_info("no optional clock %pOF:%s\n", child,
> > > + name ? name : "");
> >
> > Is this intentionally pr_info?
> Yes, it's not an error if an optional clock isn’t there.
> Would pr_debug be more appropriate?
>
>
> > > + } else if (name && index >= 0 && PTR_ERR(clk) != -EPROBE_DEFER) {
> > > + pr_err("ERROR: could not get clock %pOF:%s(%i)\n",
> > > + child, name, index);
> > > + }
> > > +
> > > return clk;
> > > }
> > >
>
> Thanks
> Phil
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